Aralia leaf stalk. Light micrograph of a cross-section through a leaf stalk (petiole) from an Araliatree. The outer layer directly below the epidermis is a supporting collenchyma ring (red), followed by the cortex (white-brown). The distinctive corrugated ring is the vascular bundles. An outer layer of yellow supporting fibres is separated from an inner layer of xylem tissue (yellow) by a dark brown ring of phloem and cambium. The large central pith (light blue) consists of parenchyma cells. Magnification: x14 when printed at 10 centimetres across.